Such a pumping device has become known from U.S. Pat. No. 4,405,294 (corresponding to German Offenlegungsschrift No. DE-OS 30,38,525).
The prior-art metering pump is designed as a reciprocating piston pump which delivers defined, adjustable delivery volumes from a feed line into a discharge line and from there to a user during the pump stroke.
Such metering pumps are used for the highly accurate, reproducible feed of liquids which are needed especially in medical engineering for performing anesthesia. It is important to maintain the amounts metered as accurately and reproducibly as possible in order to subsequently feed anesthetic to be evaporated into a carrier gas stream and thus to reach an anesthetic concentration in the carrier gas that is determined by the metering pump. However, it was found that especially in the case of low-boiling anesthetics, the feed strokes increasingly generate a vacuum in the liquid, so that gas bubbles are formed and undesirably entrained, which jeopardizes the accuracy of metering. In addition, readily boiling liquids are able to produce considerable amounts of gas in the feed lines, which make continuous metering of liquid impossible, even at room temperature.